The present invention relates generally to gas turbine engines, and, more specifically, to airfoil manufacture therefor.
A turbofan gas turbine engine includes a fan having a row of fan blades extending outwardly from a supporting rotor disk. The fan is powered by a turbine which extracts energy from combustion gases generated in a core engine for producing thrust to power an aircraft in flight.
Minimizing engine weight for an aircraft application is a primary design objective. However, weight reduction is itself limited by the requirement to maintain component strength under the various loads experienced during operation.
For example, the fan blades are relatively large and generate significant centrifugal force during rotor operation. The blades must be designed to withstand both centrifugally induced loads and stress as well as aerodynamic loads as ambient air is pressurized for generating propulsion thrust.
Maximum fan blade size is limited by the high strength materials available for the manufacture thereof, and the associated cost of manufacture. All-metal fan blades, such as titanium, have high strength yet are expensive to manufacture. All-metal fan blades are also relatively heavy which correspondingly increases the size and strength requirements of the supporting dovetails thereof and rotor disk.
Composite fan blades formed of high strength graphite fibers in a carbon matrix enjoy high strength at reduced weight over all-metal fan blades. However, composite fan blades are expensive to manufacture, and must be specifically configured to provide directional strength for enjoying a suitable useful life.
Hybrid fan blades are being developed for reducing weight while providing suitable strength. A typical hybrid blade has a metal body, such as titanium, with weight reducing pockets preferentially formed in one side thereof. The pockets are filled with a suitable elastomer to complete the required aerodynamic contour of the airfoil portion of the blade for acceptable aerodynamic performance. The metal portion of the blade provides the required strength, with metal being removed in the pockets for removing weight without compromising overall strength of the blade.
One manner of making hybrid blades includes machining the desired pockets in the pre-formed or pre-forged airfoil as its contours are machined. Elastomer in the form of a paste or putty is positioned in the respective pockets. And, a pair of contoured forming tools or dies are disposed on opposite sides of the blade for pressing the elastomer in the pockets to undergo curing. However, this manufacturing process is complex and expensive, and is not practical for producing hybrid blades in large quantities.
Accordingly, it is desired to provide an improved method of making hybrid gas turbine engine airfoils at reduced cost.